A recent rise in multimedia computer applications has increased the demand for compact projectors that are powerful enough to display brightly computer-generated presentations to large groups of people, yet portable enough to be carried easily from venue to venue. These projectors typically use a lamp, mounted within a mirrored parabolic reflector, to generate a bright beam of light. In the past, these reflectors tended to be metal, however, recently glass reflectors have been preferred due to the insulating properties of glass.
As the size of these projectors has decreased, and the intensity of the projector lamps increased, problems have occurred with heat dissipation from the lamps. Where heat is not dissipated sufficiently, lamps may run at higher than intended operating temperatures, which may cause the lamps to burn out prematurely, or possibly explode. In addition, temperatures within the projector may rise and cause surrounding components to melt or be otherwise damaged by the heat, possibly resulting in a catastrophic failure of the projector.
One solution to this overheating problem for projectors with metal reflectors is to position holes within the reflector to allow cooling air from an associated cooling fan to circulate through the reflector and draw heat away from the lamp, as shown in U.S. Pat. No. 4,053,759. Because the reflector of U.S. Pat. No. 4,053,759 is metal, it would have been possible to form the holes disclosed therein using conventional drilling, sawing, grinding, and/or punching techniques.
However, no suitable technique exists for cutting a ventilation hole in a glass reflector. Molded glass reflectors are more fragile than metal reflectors, and easily fracture or shatter when machined using conventional drilling, sawing, grinding, and punching methods.
An example of another cutting device, the water jet cutting machine, is disclosed in U.S. Pat. No. 5,273,405, the disclosure of which is herein incorporated by reference. A typical water jet cutting machine, such as the machine described in U.S. Pat. No. 5,273,405, is designed to produce a water jet at between 25,000 psi and 100,000 psi. At these high pressures, the water jet is unable to pierce a hole in the middle of a surface of a molded glass reflector without frequently fracturing the reflector upon impact of the water jet with the reflector surface.
Fracture rates of about 10% are commonly experienced at 25,000 psi, requiring about 10% of the reflectors to be discarded. Molded glass reflectors are expensive components, and this high discard rate renders current water jet cutting methods commercially infeasible. In addition, current water jet cutting methods may damage those reflectors that do not visibly break by producing tiny stress fractures from the impact of the high pressure water jet, which negatively affect the structural integrity of the reflector. Therefore, current water jet cutting methods are inadequate for glass reflectors.
To reduce the problems associated with dissipating heat from projector lamps, it would be desirable to provide a cutting method capable of producing a ventilation hole in a glass reflector.